1. Field of the Invention
The present invention relates to a reverse flow prevention apparatus for use mainly in a directly-connected water distribution system.
2. Description of the Related Art
As a conventional apparatus of this type, there is cited a pressure-reduction type reverse flow prevention apparatus a as shown in FIG. 10. The pressure-reduction type reverse flow prevention apparatus a is provided with first and second check valves d, e, which are installed upstream and downstream, respectively, in a flow path c formed inside a casing b thereof and which operate independently from each other, and is further provided with an intermediate chamber g equipped with a pressure regulator mechanism f between the first and second check valves d, e.
The pressure regulator mechanism f is provided with a bypass h linking the intermediate chamber g with a portion of the flow path c, on the upstream side thereof, and is capable of adjusting a pressure inside the intermediate chamber g so as to be always lower than a pressure on the upstream side and higher than that on the downstream side by blocking up the bypass h with a diaphragm i, and linking an escape valve k for opening and closing a drain outlet j of the intermediate chamber g with the diaphragm i through the intermediary of a valve bar m.
However, the pressure-reduction type reverse flow prevention apparatus a described above has a problem that it becomes large in size and heavy in weight because it is provided with the pressure regulator mechanism f which is mechanically independent, that is, the bypass h, the escape valve k, and so forth.
Further, the pressure-reduction type reverse flow prevention apparatus a has another problem in that pressure loss therein is very large because the same is constructed such that a pressure inside the intermediate chamber g is lessened to a level lower than that on the upstream side thereof due to magnitude of a spring load of a first check valve spring n of the first check valve d, that is, because a condition is set such that a resistance at which the first check valve d is opened by flow of water is rendered large, and a pressure inside the pressure-reduction type reverse flow prevention apparatus a is caused to fall gradually from the upstream of the flow path c towards the downstream thereof.